1. Field of the Invention
The present invention relates generally to delivery of hot mix asphalt for road bed construction and more particularly to an assembly and method for insuring desegregation of the hot or warm mix asphalt prior to its application to the road bed.
2. Description of the Prior Art
Hot mix asphalt (HMA) is typically prepared off-site from the road bed being constructed. It is then transferred to a transport machine which may be a dump truck and then either to a material transport vehicle or directly to a paving machine. In any case, the HMA is often elevator conveyed to a spout from which it falls into the truck bed. Next, it exits a chute at the back of the truck usually into some sort of hopper. From there it is conveyed and falls from the conveyor either directly into a paving apparatus from which it exits onto the road bed or into another hopper where it is temporarily stored until a paving machine is ready to use it. The HMA is between 300 and 450 degrees Fahrenheit.
Through the transport process more and more larger heavier pieces of HMA roll to the outside of any pile or peak of HMA. The material also has a temperature variation because the material on the outside of the truck cools faster then the material in the middle of the truck. Due to this segregation, roadbeds constructed will not be uniform and their durability will be severely reduced. Because each transport step allows this gravity-effected segregation of the HMA to occur, a number of devices have been derived which operate to desegregate the HMA prior to its roadbed application, however, these prior devices although an improvement over gravity alone, still do not create the uniform HMA distribution that is desired.
U.S. Pat. No. 5,405,214 for a Paving Machine Incorporating Automatic Feeder Control Gates uses a first gate mechanism and a second gate mechanism. Raising one and lowering the other shifts discharged materials to one side; raising and lowering the opposite shifts the material to the other allowing management of the flow along both a vertical and horizontal plane. Some mixing also occurs as a result.
U.S. Pat. No. 5,553,968 for a Method and Apparatus for Conveying and Desegregating Aggregate uses a different approach. Rather than using adjustable gates to move outer materials to the center for remixing, this one uses a notch in the floor of a first drag slat conveyor. The notch is in the center of the first conveyor floor and positioned near the end of the first conveyance path. The small pieces fall through the notch on to a second conveyor, the large pieces fall later thereby re-orienting the small and large pieces along the direction of the conveyor, rather than outside to inside.
U.S. Pat. No. 5,642,961 for a Method for Conveying and Desegregating Aggregate is similar to the U.S. Pat. No. 5,553,968 in that it reorients laterally segregated aggregate on a conveyor to a longitudinally segregated aggregate. The aggregate is then desegregated as it comes into contact with and travels along a second conveyor. This is achieved by discharging smaller pieces onto the second conveyor before the larger.
In U.S. Pat. No. 6,007,272 for an Asphalt Paver with Remixing Conveyor System a paver which includes a hopper conveyor to move HMA from hopper to screed is disclosed as having at least one pair of spaced apart axially rotatable augers. These augers are disposed in the direction of travel. Each auger has a “tapered peripheral diameter” defining a space therebetween as a “remixing zone”.
U.S. Pat. No. 6,481,922 to Boyd specifically teaches a device wherein the outer portions of a moving HMA stream are moved toward the center via augers. Here, the outer portions of the HMA stream drops through a material outlet with the inner portions of the stream. This patent terms the uncovered center portion of the augers which is positioned directly over the material outlet a mixing zone disclosing that this is the area where mixing the small and large pieces of HMA occurs. In truth, very little mixing occurs but, rather, the outer and inner portions of the stream are simply concentrated to fall together through a smaller opening. While this necessarily does result in some remixing of some pieces of HMA, this device does not adequately address the need for a uniform HMA mixture.
Finally, U.S. Pat. No. 5,035,534 includes transversely disposed variable pitch screw augers on a single shaft mounted in the bottom of storage hopper. The first screw auger is located on one side of a mid portion of the shaft and the second is located on the other side of a mid portion of the shaft. Each of the screw augers has flights of a first pitch at the outer end of the shaft and flights of a second pitch set inwardly. This arrangement is disclosed as allowing the HMA at the center portion of stream to combine with material transported inwardly to center. The disclosure states that the variable pitches allow different sizes of HMA pieces to be mixed and specifically discloses that the mixing occurs due to and in the flights of the pitched augers. The material is mixed in the flights and moved toward the center where it falls through the material outlet underneath a cover.
It is a first object of the present invention to create a desegregation system that improves the desegregation of the HMA over previous inventions;
It is a second object of the present invention to create an augering system that more completely mixes HMA within and between its auger flights;
It is a third object of the present invention to devise means to better divert the small pieces of HMA from a midportion of the conveyed stream of HMA to the outer portions of the stream;
It is a fourth object of the present invention to create a way for the diverted HMA to be more completely blended with all portions of the HMA which is not diverted;
It is a fifth object of the present invention to provide an output stream of HMA that has a flatter profile rather than highly peaked in the middle.